Hi all. I have a new chrome alternator on my project and it SHOULD be in perfect condition however I have noticed the sense wire is drawing nearly .2 amps. I don't know enough to know if that's a large amount of current or if its normal or what. At the moment the relay/check lamp wire is not connected however this should not affect things as with ignition OFF it wouldn't have 12v anyway. I'm well out of my depth and uncle google isn't too helpful either. Wired like this Cheers!
I always thought the sense wire was not supposed to be jumped directly over to the Alt Batt wire, as system votlage would not be accurately read. I hook mine to the Igntion switch HOT. I thought the sense wire was to read system voltage from an electrically distant location, not direct Batt voltage as shown in your schematic. I have also seen many cars wired just like your Alt schematic shows, so it does work, but I just don't think that is the way its supposed to be wired. Im sure there are many people on this forum with way more technical expertise than I , that that can provide a better explanation.
Correct. The #2 sense wire should run parallel with the alternator output wire to the main power distribution location. This allows the alternator to provide 14.4 volts there, instead of at the back of the alternator, eliminating any voltage drop to the system. To flyingbrick's original question, I don't know what the correct sense wire amperage should be, or whether changing the wiring would make any difference, but .2 amp doesn't sound problematic.
No one is going to like this but I normally run mine without the exciter wire. it doesn't start charging until you rev it once but its going to get revved anyway.
The way that is wired it will be excited all the time. The field should only be hot when the key is on.
One advantage of running an exciter through an idiot light is warning of an output problem. An example is when I noticed the voltage of my 10 SI sometimes seemed lower than usual at idle, but when I peeked under the dash and saw the indicator light (common #193) barely glowing while at idle, I knew there was a problem, and found a diode was bad during the rebuild.
I actually kept my idiot light when I built my S truck back in the '90s. I actually do like a light, aside from letting you know that you are or are not charging they also let you know if the key is on. I have killed a motor and walked away without the key being turned to the off position before.
The idiot light will light very dimly when the DIODE TRIO is bad inside the alternator. Mine lit up like this, and was noticeable at night, and the output was 15.3 volts. I changed the Trio and the light behaved as normal.
Get the factory wiring diagram and wire accordingly. The jumper is bogus, and will result in a power draw even with the key off.
Sorry, I should have stated that I don't have the jumper as depicted (that's just a random drawing I found ). The car hasn't been run yet and currently there is no lamp connected to the indicator wire...but there will be. I do have my sense wire looped down to the batt cable stud- I'll extend that right down to the battery terminal to be safe (but it won't stop that .2 amp draw) Does anyone know how long it would take that .2 amp draw to flatten a battery? I'm a fitter/turner/welder and electrical stuff us gibberish to me. Next question! Can I use an LED as my warning lamp? Or will it not draw enough current to excite things.
I used an LED on a custom dash I built once, it was a 24 volt but it lit up and let me know my switch was on and that my alt was alting. I don't know if the draw was enough to excite my alternator. a .2 amp draw? or a 2 amp draw? it is hard to measure amp draw without it being under load and I would think that .2 amps would be negligible at best.
Thanks guys. Yes its a .2 amp draw ( .18 actually) with everything else off. It was just the last place I expected to see current draw. I have rewired the whole front end and half the cabin- with the vehicle off that sense wire is the only thing that may draw the battery down. 24v led is a good idea! I'll try that if the 12v one I have doesn't work Hope you all have a good day! Cheers, Nathan , nz.
The way the indicator light works is you have some electric flow (ie from ignition hot source to alt) when it is not charging, and the light is lit up. But when it is charging, the voltage balances and the exciter circuit has essentially no flow so the light is not on. I think you are checking with the engine off. Start the engine and then check, I think you will find no amps.
It is not the indicator wire that is drawing current, its the sense wire. My understanding is that the indicator wire is as good as disconnected when the car is off anyway (the other side of the lamp gets ignition switched +12v) With the car off, the indicator wire just goes to a lamp and the other side of the lamp is open...not grounded or anything. Could be wrong, happy to hear peoples thoughts, I only know what I do from reading on google.
Depending how good a battery you have it will be too weak to start the car after 2 weeks and dead as a door nail if you leave it for 2 months.
So one option is to install a relay in the sense line that closes with ignition. Or I could take the alt in for repair..hmmm
I don't think there should be any sense wire current draw when off, so I would have a repair shop check out the alternator.
If you want to put an LED for the indicator, you may want to put a resistor (100 ohm, 1 Watt) inline, then wire the +12V LED across the resistor. (+ side of LED toward ignition switch wiring). When the alternator starts to charge both sides of the LED are at the same potential and the light goes out.
The reason I used a 24v was because the wife works at an electronics firm and what they build works off of 24v most of the time. So it was available. an LED doesn't draw many amps and I think that is the only reason it worked on 12V.
You don't need any relay, just wire it by the factory wiring diagram. 3 wires, it could hardly be simpler. Or, connect the field wire to something that is OFF when the key is off and ON when the key is on.
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